The present invention relates to a wireless communication system using frequency hopping, as well as to a method of controlling this system.
Frequency hopping is a method for performing communication while changing frequencies in accordance with a predetermined rule. The predetermined rule is called "frequency hopping pattern", and the changing frequencies are called "frequency channels".
There are a variety of methods of selecting a frequency hopping pattern. One method is to store frequency hopping patterns in a non-volatile memory, such as a ROM, and use an appropriate frequency hopping pattern selected from among those stored. If there is a controlling station, the controlling station may determine an arbitrary frequency hopping pattern.
Not limited to frequency channels used in frequency hopping communication, same frequency channels are used as control channels since it is necessary to exchange control information; alternatively such as line control information, means for controlling each frequency channel in time division to set a period for communicating control information and a period for communicating data is provided.
Further, in a conventional frequency hopping transmission, as shown in FIG. 17, one frame is divided in time division into a control information period (LCCHT) when a controlling station sends control information to a terminal, a data communication period for communicating audio data and other data (audio channel and data channel), and another control information period (LCCHR) when the terminal sends control information to the controlling station. Further, in the control information period (LCCHT), each frequency which is used in one period of a frequency hopping pattern is assigned to one terminal. Therefore, the terminal with which control information can be exchanged in the control information period (LCCHT) in one frame is fixed. The controlling station transmits information addressed to a terminal with which control information can be exchanged via a frequency channel, and each terminal transmits control information to the controlling station when a frequency channel assigned to the terminal is used in a control information period (LCCHR) in a frame.
However, in the above conventional method, a terminal which can communicate with the controlling station is fixed for each frequency channel used in the frequency hopping pattern, and has to call a destination station via the controlling station when starting communication, and thus the load on the controlling station is very large.
A conventional operation when a terminal 1 is trying to communicate with a terminal 2 is explained below.
1) A terminal 1 notifies the controlling station by control information indicating that terminal 1 wishes to open communication with a terminal 2 in a control information period (LCCHR), using a frequency channel assigned to terminal 1, in a control information period (LCCHR) in a frame.
2) The controlling station notifies terminal 2 of the control information indicating that terminal 1 wishes to open communication with the terminal 2, in a control information period (LCCHT), when a frequency channel assigned to terminal 2 is used in a control information period (LCCHR) in a frame.
3) Terminal 2 sends to the controlling station control information indicating whether it is possible or not to open communication in a control information period (LCCHR) when a frequency channel assigned to terminal 2 is used in a control information period (LCCHR) in a frame regardless of whether or not terminal 2 can communicate or not.
4) In a case where terminal 2 cannot open communication, the controlling station sends to terminal 1 control information indicating that it is not possible to communicate with terminal 2 in the frequency channel assigned to terminal 1.
Further, in a case where terminal 2 can open communication, the controlling station decides on a frequency hopping pattern necessary for communication between terminal 1 and terminal 2, then notifies terminal 1 of the frequency hopping pattern in a control information period (LCCHT), via the frequency channel assigned to terminal 1 as well as notifies terminal 2 of the same information, in a control information period (LCCHT), via the frequency channel assigned to terminal 2.
5) Terminal 1 and terminal 2 communicate using the frequency hopping pattern notified by the controlling station.
In the conventional communication system, the controlling station has to communicate with each terminal via frequency channel assigned to the terminal, and so the load on controlling station is considerably large. Further, it takes time to open communication between terminals. Furthermore, there is a problem in that it is difficult to lower the price of the controlling station.